A wafer used as a basic material for semi-conductor is proceeded steps of ingot grow, slicing, lapping, cleaning and polishing before it is ready to be used. A series of checking and measuring are taken so that the thin wafer meets the requirements of the customers. Generally, the thickness of a thin wafer is only few mils and fragile. It is not possible to carry the thin wafer by robots or manual to test, ship and/or proceed. The thin wafer is put on a carrying device for convenience of shipping or testing.
As shown in FIG. 1, a thin wafer 90 to be test is put on a carrying device 91 which includes a plurality of tiny holes 92 defined therethrough and a vacuum system 93 is used to suck the air in a chamber 94 in the vacuum system 93 and the tiny holes 92 so as to attract the thin wafer 90 on the carrying device 91. Therefore, a probe 96 of a detection device 95 can lower and access the thin wafer 90 to proceed series of checking processes. The bottom of the thin wafer 90 in contact with the carrying device 91 is ground for convenience of test.
The conventional carrying device 91 is made of silicon carbide which is stiff with high yield strength and flat so that the thin wafer 90 can be snugly attracted on the carrying device 91 without sliding. The thin wafer 90 can be well supported on the carrying device 91 having the tiny holes 92 even if the probe 96 touches the thin wafer 90. Nevertheless, the silicon carbide is expensive and poor of electric conductivity and heat conductivity. Therefore, a circuit without front side ground is impossible to be tested by using silicon carbide.
Referring to FIGS. 2 to 3B, aluminum is used as the carrying device 100 which is less expensive compared with the silicon carbide and includes better heat conductivity and electric conductivity. Although the yield strength of the aluminum carrying device 100 is lower than that of the silicon carbide, it is strong and can be machined to have a smooth surface. However, it is difficult to drill holes in the aluminum carrying device 100 so that the manufacturers set grooves 102 on the surface of the carrying device 100 and the holes 101 are drilled at the cross points of the grooves 102. The vacuum system 93 sucks the air in the holes 101 and grooves 102 to attract the thin wafer. When the probe 96 touch the area of the thin wafer 10 where the grooves 102 or holes 101 are located, the thin wafer 90 tends to be bent due to less support at those positions. Besides, if the sizes of the holes 101 and the grooves 102 are larger than that of the chips of the thin wafer 90, the chip cannot be ground properly.